1. Field of the Invention
This invention relates to single lens reflex cameras and viewfinders for single lens reflex cameras in which data images are displayed with the image of a scene by passing data light into the camera's pentaprism, and more particularly to display changing devices for such viewfinders.
2. Description of the Prior Art
In general, automatic exposure cameras may operate in one of two modes, namely a shutter time priority mode or an aperture priority mode. In so-called dual priority cameras, operable in either one of these modes, the display of exposure information in the camera's viewfinder must be switched depending upon the selected exposure mode. That is, in the shutter time priority mode, it is necessary to display the preset value of the shutter time and an aperture value computed on the basis of the object brightness. Conversely, in the aperture priority exposure mode, the viewfinder must display the preset aperture value and the shutter time computed on the basis of the object brightness. However, such data may each be displayed by using a meter with a scale. In the shutter priority mode, the exposure data may be displayed at one side margin of the field of view image. In the aperture priority mode, the exposure data may be displayed in the lower margin of the field of view image. If both exposure data appear simultaneously, the displayed data may be confusing to the photographer. In other words, when the exposure data are to be displayed in such a manner, it is desirable to control the presentation so that one set of data is displayed and the other is extinguished.
Various types of display switchover devices for presenting and cancelling exposure data are known. These may use a changeover mechanism which is actuated by an operating member provided in the camera body for extinguishing the displayed data. However, conventional switchover devices generally involve placing a shutter member in the data light path to make the displayed information disappear, and by operatively connecting the operating member to the shutter by means of wire or other device. Therefore, conventional switchover devices in a finder raise the problem of increasing the size of the finder to allow for space in which the shutter member may move. This complicates the mechanism. Furthermore, because the operative connection between the shutter member and the operating member in such switchover devices must be established with the use of a wire or the like, it cannot be used with interchangeable finders decoupleable from single lens reflex cameras. In prior single lens reflex cameras using interchangeable viewfinders, such display switchover devices had to be located entirely within the camera body, thereby sacrificing the simplicity of the latter.